How do we know that Jesus is a priest forever?

The permanence of Christ's priesthood is affirmed in Hebrews 7:20-21, where it states that Jesus became priest by an oath made by God, who declared, 'Thou art a priest forever after the order of Melchizedek.' Unlike the Levitical priests, who were many and could not remain in office due to death, Jesus has an unchangeable priesthood because He lives forever. This assures believers that He is able to save completely those who come to God through Him, as He intercedes for them eternally, emphasizing His unique role as the guarantor of a better covenant.